Khelben Blackstaff wrote: > Hello Mr. Rees and thank you for replying. > > I have read this post and it is very good but it mentions alignment > of the partitions using special CHS values and LVM/ext4 options. Yes, and that seems to be the only way to align partitions to a 128k boundary. You do need to use such rules to create aligned partitions. Then, you need to align RAID created from such partitions to 128k Blocks, by setting the chunk-size to 128k: "mdadm --chunk=128k" ( well, a multiple of that, anyway ). And, then, align LVM ( with the --dataalignment option for pvcreate ) and the Filesystem ( with the -E stripe-width= to the mkfs command ) to such boundaries as well. That applies to ext3 AND ext4 filesystems AFAIK. > My partitions and both LUKS/LVM are aligned properly (at least i think > they are). I am worried about the alignment of RAID itself. On that link I read this comment: If your SSD has an 128k erase block size, and you are creating the file system with the default 4k block size, you just have to specify a strip width when you create the file system, like so: # mke2fs -t ext4 -E stripe-width=32,resize=500G /dev/ssd/root So, to align your Raid to the SSD boundary, you need to use the "stripe- with" parameter while creating the filesystem. Assuming the partition start has been set to a 128k boundary as commented before. > 2010/1/4 David Rees <drees76@xxxxxxxxx>: >> On Mon, Jan 4, 2010 at 11:30 AM, Khelben Blackstaff >> <eye.of.the.8eholder@xxxxxxxxx> wrote: >>> Is there a way to make the RAID data start at a particular offset ? >>> (In my case 512 sectors) ? >> >> http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds- erase-block-size/ >> >> May have to tweak your fdisk parameters a bit. >> >> Don't worry about aligning your /boot partition since you don't >> read/write from that much. >> >> -Dave -- Antonio Perez -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
